Power from night sky

Print edition : October 25, 2019

Schematic of night-time thermoelectric generator. Photo: Aaswath P. Raman (UCLA), Wei Li and Shanhui Fan (Stanford U)/Joule (CellPress)

A team of engineers from the University of California at Los Angeles (UCLA) and Stanford University, led by Aaswath P. Raman of UCLA, has developed a new device that harnesses the temperature difference between the earth and outer space to function as an electricity generator at night enough to light an LED lamp. The work has been reported in the online journal “Joule”.

The device is a thermoelectric generator that generates electricity when one side of the generator is cooler than the other. To demonstrate the potential of night-time power generation using radiative heat exchange with space, the researchers built and tested a low-cost thermoelectric generator on a clear night in late December 2017 on a rooftop in Stanford. The cold side was coupled to a simple black emitter (a 20-cm aluminium disk painted with a commercial black paint) facing the sky which was attached with heat transfer paste to the cold side of a commercial thermoelectric module. The hot side of the module, heated by the ambient by natural convection, was coupled to a small aluminium block attached to a 20-cm aluminium disk with multiple fins outside the enclosure. The whole device included a polystyrene enclosure covered in aluminised mylar (to minimise thermal radiation from the enclosure) and an infrared-transparent wind cover made from 12.5 micrometre-thick low-density polyethylene. The cold side got cooler by a few degrees than the hot side and the generator produced up to about 25 milliwatts/square metre of the device, enough to light a small light-emitting diode, or LED, bulb. The team estimates that further design improvements, such as better insulation around the cool top plate, could boost production up to at least 0.5 watts/sq. m.

Raman, a materials scientist, also envisions using their team’s generator to help power remote weather stations or other environmental sensors. This may be especially useful in polar regions where there is no sunlight for months together.

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